The insulin resistant (IR) syndrome is associated with an increased incidence of hypertension and cardiovascular (CV) disease. Data from the applicant's laboratory suggests that endothelial dysfunction may be the mechanism that links IR to CV disease. Previous studies show impaired endothelium-dependent relaxation in small mesenteric and coronary arteries from IR rats. This dysfunction appears to be secondary to a defect in endothetium-derived hyperpolarizing factor (EDHF). These data support the existence of a situation where the EDHF dilator component is selectively impaired and provides a model to assess mechanisms leading to impaired EDHF function. Moreover, it provides us a model to assess compensatory responses of other endothelium derived relaxing factors to an EDHF deficit. The overall hypothesis to be examined is that impairment of endothelium-dependent dilator capacity occurs during IR. Specific hypotheses to be tested are (1) Endothelium dependent relaxation is impaired in small mesenteric arteries to physiologic as well as pharmacologic stimuli. (2) Restoration of normal endothelium function occurs after cessation of fructose-rich diet. (3) Endothelial dysfunction associated with IR is due to a decreased production of EDHF. (4) Decreased substrate availability and/or abnormally low levels of cytochrome P450 (CYP) isoforms account for decreased EDHF production. (5) Endothelial dysfunction associated with IR is due to decreased sensitivity of potassium channels on vascular smooth muscle to EDHF. (6) The NO and prostacyclin systems do not compensate for this loss of dilator capacity. To test these hypotheses, two specific aims will be addressed. Specific aim 1. Characterize the nature of impaired vascular function in insulin resistance. First, we will assess whether IR induced impairment of endothelium-dependent relaxation is stimulus dependent. Second, we will explore the vascular effects of insulin in the setting of IR. And third, we will determine the vascular characteristics of reversal of endothelium dysfunction after cessation of fructose feeding. Specific aim 2. Determination of the mechanism of impaired endothelium-dependent dilation in insulin resistance. First, we will investigate the effect of lR on dilator responses to exogenous arachidonic acid. Second, we will explore the effects of IR on synthesis of bioactive metabolites of arachidonic acid. Third, we will examine the relationship between endothelial function and levels of CYP and NO synthase protein. Fourth, we will determine the effect of application of exogenous arachidonic acid metabolites (epoxyeicosatrienoic acids) on vascular tone. These data will determine mechanisms of endothelial dysfunction in IR. Moreover, the specific role of EDHF and mechanisms for its dysfunction will be determined. This project employs physiologic, cellular, and molecular biology techniques to address the proposed questions. Findings from this project may provide important information that can be used to design treatments to prevent the cardiovascular complications of IR.